Femtosecond Refractive and Absorptive Nonlinearities Due to Real Carriers in GaAs

The carrier dynamics in GaAs following injection with femtosecond pulses above the band gap has been a topic of interest for several years.1−5 Information on carrier scattering and thermalization has been obtained and recent Monte Carlo simulations have achieved some success at explaining these induced absorption measurements.6,7 In the present work, we report the first femtosecond spectroscopic measurements of both the real part and the imaginary part of the carrier-induced nonlinear refractive index of GaAs. Our results are useful for the design of ultrafast devices using these optical nonlinearities and bring new knowledge on hot-carrier many-body effects. We focus on instantaneous band gap renormalization and plasma screening of electron-hole interactions in the 850-920-nm region, and on the short-lived resonance in the 580-750-nm region.